The present invention relates to a marine vessel comprising a hull, which includes at least one load carrying facility defined by at least one loading space with a given height, a given width and a given length, which loading space is provided on a bulkhead deck, and a propulsion arrangement, which includes at least one steerable thruster unit connected by a shaft arrangement to a drive means.
In load carrying marine vessels, such as double end ferries, the propulsion arrangement may include one or more steerable thruster units for propelling and improving maneuverability of the vessel. Such thruster units are usually powered by electric motors or internal combustion engines, e.g. diesel engines. Freighters, container ships, RoRo and RoPax (RoRo passenger) are examples of other types of marine vessels in this context.
When the thruster is powered by an electric motor the motor conventionally is arranged directly overhead the steerable thruster unit, whereby it may be on or extending through the bulkhead deck. Power is transmitted to the propeller of the steerable thruster unit by means of a so-called L-drive unit comprising a drive shaft extending from the electric motor into the thruster, and in the thruster connecting to an angle gear and a propeller shaft with a propeller.
When the thruster is powered by an internal combustion engine the engine conventionally is arranged further into the ship, whereby the shaft line or gear box connected thereto as well as the engine may be on or extending through the bulkhead deck. Power is transmitted to the propeller of the steerable thruster unit by means of a so-called Z-drive unit comprising a shaft line extending from the internal combustion engine towards the steerable thruster unit, a gear box with an angle gear arranged directly overhead the steerable thruster unit, a drive shaft extending from the gear box into the thruster, and in the thruster connecting to a second angle gear and a propeller shaft with a propeller.
In practice, especially with high power steerable thrusters, this means that either the electric motor or the internal combustion engine form large obstructions extending through and rising above the bulkhead deck which in the above mentioned type of marine vessels typically would be the main car deck. This clearly is problematic in view of loading and unloading, and also with regard to availability of loading space. Considering that the loading space on the bulkhead deck has a given width, a significant part of the given width is occupied by the usually rather voluminous or bulky electrical motor, gear box or engine housings, either in the middle (in the case of a vessel with a single thruster) or one on each side of the marine vessel (in the case of a vessel with two thrusters). This reduces the number of available lanes on the loading or unloading ramps as well as the available loading space, which makes cargo loading and unloading slow and also complicates the distribution of cargo on the bulkhead deck.
The term bulkhead deck, which has been used above and will be used further on, has a definite meaning in shipbuilding. In the present application, however, this term should be understood in a more general manner, i.e. representing the main car deck, RoRo-car deck, or main cargo deck on a marine vessel. In the following the term upper deck will also be used. This term also has a definite meaning in shipbuilding. In the present application, however, this term should be understood in a more general manner, i.e. representing a deck above the one or more loading spaces on top of each other on a marine vessel.
The object of the present invention is to provide a marine vessel by which the above mentioned disadvantages are avoided and which provides facilitated and faster loading and unloading as well as maximizes the utilization of the loading space.